1. Field of Invention
The invention relates to a dielectric antenna component, in one embodiment by which an internal multiband antenna of a small-sized radio device can be implemented. The invention also pertains to such an entire antenna.
2. Description of Related Technology
In many small-sized radio devices, such as most models of mobile phones, the antenna is placed inside the casing of the device for convenience. A very common internal antenna type is the planar antenna, which has a radiating plane and a ground plane, isolated from each other by air. Efforts are naturally made to make the internal antenna as small as possible. The size compared to an air-insulated antenna can be reduced by using dielectric material under the radiating plane. The central part of the antenna is then a chip component partly coated with conductive material, which can be mounted on the circuit board of a radio device. The higher the permittivity of the material is, the smaller the antenna element having a certain electrical size is physically.
When a radio device must operate in at least two systems, the frequency bands of which are relatively far from each other, the antenna structure becomes more complicated in comparison to a single-band antenna. One solution is to use two separate antennas for example in such a way that there is one chip-type antenna component for each band, in which case the bands can be formed and tuned independently of each other. However, the additional space required by the other antenna on the circuit board of the device is a drawback. In addition, the feed of the antennas from a shared antenna port requires additional components, which take their space and increase the costs.
FIG. 1 shows a typical prior art dielectric antenna (from the publication JP 2001217631), which can be implemented as a dual-band antenna. The antenna component is on the circuit board PCB of a radio device with its lower surface against the ground plane GND belonging to the circuit board. The component comprises a dielectric substrate 110 and two radiating antenna elements on its surface. The main element 120 covers part of the upper surface of the substrate 110. The feed conductor 111 of the antenna runs on a side surface of the substrate and joins galvanically the main element at its one end. The other antenna element 130 is parasitic. It covers another part of the upper surface of the substrate and is galvanically coupled to the ground plane by a short-circuit conductor 112 running beside the feed conductor. In addition, the main element extends to the end surface of the substrate, and the parasitic element to the opposite end surface, on which end surfaces they have a capacitive coupling to the ground GND for increasing the electrical size of the element. Between the main and the parasitic element there is a slot on the upper surface of the substrate, over which the parasitic element obtains its feed electromagnetically.
The lower operating band of the antenna is based on the resonance of the main element 120, and the upper operating band is based on the resonance of the smaller parasitic element 130. In addition, the harmonic frequency of the main element can be utilized in certain cases by arranging it in the range of the upper operating band for widening it. The harmonic ratio can be adjusted by means of perforation provided in the basic element. The parasitic element is also perforated, which provides one possibility for tuning the resonance frequency of the parasitic element.
The component included in the solution according to FIG. 1 has the drawback that for a dielectric antenna component, it is relatively large-sized and hence consumes considerable space (and may have appreciable weight). Furthermore, the tunings of the antenna elements have an effect on each other, which makes tuning more difficult and increases production costs.
Accordingly, it would be desirable to provide an improved antenna component (and antenna) solution that is space efficient, and which substantially decouples the antenna elements in order to facilitate easier tuning and matching.